1. Field of the Invention
The present invention relates to a magnetic tape cassette loaded with a thinner magnetic tape for long time recording having a structure capable of detecting a tape end of the thinner magnetic tape accurately.
2. Description of the Related Art
FIG. 5(a) is a plan view of a magnetic tape cassette loaded with a magnetic tape (hereinafter referred to as a xe2x80x9ctape cassettexe2x80x9d) composed of an upper half cassette housing 1D and a lower half cassette housing 2D, wherein an upper half cassette housing 1D is removed. FIG. 5 (b) is a side view of the tape cassette from a supply reel side. FIG. 5(c) is a side view of the tape cassette from a take-up reel side.
In FIG. 5(a), a tape cassette DD is composed of a lower half cassette housing 2D, a light exit 3D on the side of a supply (SP) reel 5D, a light exit 4D on the side of a take-up (TU) reel 6D, the SP reel 5D for supplying a magnetic tape T through a tape travel path to the TU reel 6D, the TU reel 6D for winding in the magnetic tape T supplied from the SP reel 5D, a tape pad 7D for padding the magnetic tape T on a pole incorporated in the lower half cassette housing 2D for guiding the magnetic tape T to the tape travel path, a lock plate 8D for locking a front cover on the upper half cassette housing 1D not shown, a detecting light hole 9D for inserting a detecting light device P incorporated in an apparatus not shown, a pair of light holes 9Da and 9Db for passing the light emitted from the detecting light device P, light paths L1 and L2 for showing the light path of the light emitted from the detecting light device P, a pair of light exits 3D and 4D for passing the light emitted from the detecting light device P through the light paths L1 and L2 to a pair of light sensors S1 and S2 respectively.
The pair of light sensors S1 and S2 shown in FIG. 5(a) is incorporated in the apparatus for the tape cassette, such as a video tape cassette recorder (hereinafter referred to as xe2x80x9cVCRxe2x80x9d) not shown. As the tape cassette DD is loaded into a predetermined position in the VCR, the light exits 3D and 4D are opposed to the light sensors S1 and S2 respectively, within a prescribed distance.
As to the magnetic tape T for the tape cassette, each end of the magnetic tape T is connected with a transparent leader tape not shown, and another end of each leader tape is connected with a hub of the SP reel 5D and the TU reel 6D respectively.
As the tape cassette DD is loaded into a predetermined position in the VCR, the detecting light device P is inserted in the detecting light hole 9D. The light emitted from the detecting light device P passes through the light holes 9Da and 9Db respectively and forms the light paths L1 and L2, and reaches the light sensors S1 and S2 through the light exits 3D and 4D respectively.
Generally, the upper and lower half cassette housings 1D and 2D for the tape cassette DD are made of a material having lower light transmittance (such as a dark colored plastic). As the light paths L1 and L2 cross the travel path of the magnetic tape T and the magnetic tape T also has lower light transmittance, the light sensors S1 and S2 can not receive the light when the magnetic tape T crosses the light paths L1 and L2. This is a case of the tape end being undetected.
In the meantime, the leader tape is made of a transparent or semitransparent material having higher light transmittance. In this sense, as the leader tape crosses the light paths L1 and L2, the light sensors S1 and S2 receive the light from the detecting light device P. This is a case of the tape end being detected. As the amount of light, which is received by the light sensors S1 and S2, changes remarkably from less to more than a predetermined value, the tape end can be detected.
In addition, at least, if the light sensor S1 receives the light from the detecting light device P, the tape end is determined to be the last end that there is no more magnetic tape coming from the SP reel 5D, and if the light sensor S2 receives the light from the detecting light device P, the tape end is determined to be the starting end that the magnetic tape is coming from the SP reel 5D.
In case of a xe2x80x9cVHSxe2x80x9d (registered trademark) format tape cassette, the magnetic tape having a thickness in the range of 17 xcexcm to 20 xcexcm (a standard tape cassette having the recording time of 120 minutes in the standard speed mode) should have a light transmittance of 1.2% or less, and the leader tape should have a light transmittance of 50% or more. The tape end can precisely be detected by the great difference between the light transmittances of the magnetic tape and the leader tape within the above range.
As the xe2x80x9cVHSxe2x80x9d format tape cassette additionally adopted a thinner magnetic tape for long time recording of which thickness is in the range of 11 xcexcm to 13 xcexcm. For example, a magnetic tape with 11.3 xcexcm thickness has the light transmittance of 1.7% which is above 1.2%. The tape end can accurately be detected by the magnetic tape having light transmittance under 1.2% but the tape end of the thinner magnetic tape having light transmittance of 1.7% may not accurately be detected.
If the tape end of the magnetic tape cassette can not be detected accurately, it will affect the function of xe2x80x9cVHSxe2x80x9d format VCRs and maintenance of compatibility among the xe2x80x9cVHSxe2x80x9d format products (such as cassette and VCR). Accordingly, the light transmittance for even thinner magnetic tape should be kept under 1.2%.
In order to secure the light transmittance of 1.2% for the thinner magnetic tape, a light-shielding material such as carbon is admixed in a magnetic layer of the magnetic tape. Unfortunately this is accompanied by a decrease of the electromagnetic conversion characteristic. In case of even thinner magnetic tape, it becomes more difficult to maintain both the electromagnetic conversion characteristic and the mechanical strength characteristic.
Accordingly, in consideration of the above-mentioned problems of the related art, an object of the present invention is to provide a magnetic tape cassette (AA, BB, CC) used in an apparatus having a light source (P) and a light sensor (S1, S2) for detecting a tape end by the difference of light transmittance of a tape loaded in the magnetic tape cassette, the magnetic tape cassette including, a tape (T) having a magnetic layer portion for recording and reproducing information and a leader portion connecting with a reel (5, 6) for winding up and release the tape thereof, wherein the leader portion has higher light transmittance than the magnetic layer portion, a cassette housing (1A, 2A) for having the reel (5, 6) being connected with the tape (T), and a light exit (3, 4) being opposed to the light sensor (S1, S2) when the magnetic tape cassette is loaded to a predetermined position in the apparatus, for passing light from the light source (P) to the light sensor (S1, S2) through the light exit (3, 4), wherein a light path (L1, L2) of the light emitted from the light source (P) crosses a travel path of the tape (T), and wherein the cassette housing further includes an upper half cassette housing (1A, 1B, 1C) and a lower half cassette housing (2A, 2B, 2C), and a light-shielding member for shielding the light path to make light transmittance of the tape (T) being detected by the light sensor (S1, S2) at a predetermined value.
Other object and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.